"I'm unsure about the future," Stephanie Boyd said. "I know doing this is the best step."

In the still-experimental field of stem cells, the banking of umbilical cord blood has emerged as its biggest industry, driven by marketing claims that the blood could one day have the potential to cure ailments such as Parkinson's disease, paralysis and diabetes.

But there is little evidence that the promise of cord blood will ever be realized. The blood does indeed contain stem cells, but they are far different from the much-touted embryonic stem cells, which come from newly formed embryos and have the ability to become any tissue type.

That crucial distinction has been largely ignored in the marketing by more than two dozen companies around the world, most of them founded within the last five years. They have brought in hundreds of millions of dollars in harvesting and annual storage fees.

"I think the most exciting thing is that we don't know," said Dr. Charles Sims, a pathologist and co-founder of Family Cord Blood Services. "We can't say there won't be discoveries made."

The current uses of the stored stem cells are limited, and the private banks have little to show for their work so far.

The three largest cord blood businesses in the United States have collected more than 230,000 samples, generating at least $300 million in revenue from anxious parents. Just a few dozen cord blood samples have been used, primarily for children with leukemia who could have been treated with equally effective alternatives.

At Family Cord Blood Services, just one sample has been used out of the more than 9,000 collected over the last eight years. The child died.

"This is purely a commercial business," said Dr. Eliane Gluckman, a French hematologist who performed the world's first successful cord blood transplant in 1988. It is "just for profit and not for benefit."

The European Group on Ethics in Science and New Technologies, which advises the European Union, concluded last year that "the legitimacy of commercial cord blood banks should be questioned as they sell a service, which has [currently] no real use regarding therapeutic options."

Italy enacted a ban on private banking in 2003 and other European countries have prohibited any company from profiting from cord blood.

The American Academy of Pediatrics also opposes private cord blood storage.

But despite the chorus of objections, the demand for private banking is growing.

Each burst of news articles on the promise of stem cells drives more parents to bank cord blood, if only to ensure that their children aren't deprived of a chance at a cure.

It is "a therapeutic option that not everybody is going to have," said Dr. Robert Hariri, president of LifebankUSA, a Cedar Knolls, N.J., company with more than 20,000 customers.

Boyd, now a mother of two, said: "It's one-twentieth the price of a car, and it will last a lot longer."

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ALZHEIMER'S CATCHES A MOTHER'S EYE

Boyd, 23, was a few months pregnant when the fliers for baby products and services started arriving. One day a brochure from a San Bruno, Calif., company called Cord Blood Registry appeared in her mailbox.

It explained how cord blood could be used to treat dozens of blood and immune system disorders and one day might be the cure for a range of other diseases.

One word stopped her: Alzheimer's. The degenerative brain disease runs in her family. There is no cure now, but maybe cord blood could help her child decades in the future, she thought.

"I can't imagine what they are going to do with stem cells 20 years from now," Boyd said.

She searched the Web and found a dozen companies that banked umbilical cord blood.

Her mother was skeptical until Boyd explained that stem cells were the future of medicine.

While her husband, an Army sergeant, was in Iraq, Boyd settled on Family Cord Blood Services. The company impressed her with a personalized letter and an informational DVD. It offered a free year of storage for military families.

"It just felt right," Boyd said later. "I went with my heart."

A week after she signed up, a collection kit arrived. It included a blood bag, labels, clamps, a shipping box and instructions for the doctor.